Biological indicators and chemical indicators used to determine the efficacy of sterilization are well known in the art. In conventional biological indicators, a test organism which is many times more resistant to the sterilization process employed than most organisms which would be present by natural contamination, is coated on a carrier and placed in a sterilizer along with the articles to be sterilized. After completion of the sterilization cycle, the carrier is incubated in nutrient medium to determine whether any of the test organism survived the sterilization procedure. Growth of a detectable number of organisms normally takes a minimum of twenty-four hours. During this period, the supposedly sterilized articles should be quarantined.
In frequent practice, however, the hospital has neither the space for proper quarantining of the supposedly sterilized articles, nor a sufficient number of the articles themselves to permit actual quarantining. As a result, the supposedly sterilized articles are placed back into stock on the assumption that sterilization was proper and will be confirmed by a subsequent report from the laboratory.
Commercially available chemical indicators utilize chemicals which indicate sterility by color changes, or change from solid to liquid state. The advantage to such chemical indicators is that the results are known by the end of the sterilization cycle. However, those results indicate only, as in the device described in U.S. Pat. No. 4,448,548, that a particular temperature has been reached for a certain period of time; or, as in U.S. Pat. No, 4,348,209, that ethylene oxide gas was present. These devices do not indicate whether all conditions necessary to inactivate the test organism have been achieved. Only the living organism can sense the true relationships of physical and chemical parameters necessary to affect sterilization. Therefore, it is recognized in the art of sterilization that biological tests are the most accurate sterility tests.
There remains a need for a sterility indicator which will provide rapid results, yet provide a high level of confidence that all parameters, necessary to achieve sterilization, including the interrelated parameters of time, temperature and concentrations of moisture, chemicals or radiation dose, have been reached.